Bart de Boer asks about Roman numerals and constructing chords.
Scale degrees are numbered with:
when discussing only the scale degree (the note) itself. For instance:
1 2 3 4 5 6 7 * C D E F G A B C
This describes the intervals between the individual notes.
when discussing chords relative to the tonic, or key note (C is the tonic in the key of C).
So, for instance, IV would be the chord built on the fourth degree of the scale, and V would be the chord built on the fifth degree.
And yes, basic chords are built by adding notes a 3rd and a fifth above the root note. The root is whatever nbote you choose to build from (as opposed to the tonic).
For instance, to build a IV chord in the key of C, you would go to the 4th degree, F, and use that as the tonic, and add a 3rd (A) and a fifth (C) above it.
More sophisticated chords can be built up form the basic triads (three-note) chords.
The good thing about describing musical structures this way is that it gives you a set of portable realtionships. If you Know that the chord progression is I-IV-V-IV, and you know your keys, you can play that tune in any key, because you know the